Aircraft tracking systems are used for monitoring airspace for flight safety and air traffic control. Also referred to as air traffic surveillance systems, aircraft tracking systems can be deployed both as ground systems and onboard systems, and can include ground components and onboard components that communicate and cooperate with each other to provide real-time, live information about aircraft location, motion, and identification. An example of tracking technology is conventional radar.
As part of a process to modernize air traffic surveillance, conventional radar is being phased out in favor of a self-reporting scheme in which individual aircraft use satellite-based global position system (GPS) surveillance to determine their respective tracking data (e.g., position and velocity), and then broadcast the information to ground stations and possibly other aircraft within some reception range. Receivers of broadcast tracking information—both ground stations and aircraft—may then use it for various management and safety operations, such as routing and collision avoidance. The new self-reporting scheme has been developed according to a standard referred to as Automatic Dependent Surveillance-Broadcast, or ADS-B.
Under ADS-B, two different transmission link technologies have been implemented that are compliant with the standard but not directly compatible with each other. Both technologies employ radio frequency (RF) transmission and reception, differing mainly according to RF operating frequency and transponder technology, as well as certain aspects of message structure. The two technologies are Universal Access Transmitter (UAT), which operates at 978 MHz, and 1090 MHz Extended Squitter (1090ES), which operates at 1,090 MHz.
In order to bridge the incompatibility between UAT and 1090ES, ADS-B-compliant ground systems can receive messages on both technologies, and then translate and rebroadcast the translated messages on the respective technologies. A network of ground stations enables aircraft with one of the two systems to receive translated messages from aircraft with the other of the two systems via the ground system. Any two aircraft using the same system can receive messages from each other directly.